A group of microorganisms form a very complex interaction in the respiratory tract of animals. These animals can be dairy cattle, feedlot cattle, swine, and birds such as chickens and turkeys to name a few. Although the organisms can vary from animal group to animal group, they are basically bacteria such as Pasteurellae, Mannhiemae, and Haemophilus groups, Mycoplasma, and viruses of the respiratory groups such as bovine respiratory syncytial virus (BRSV), bovine viral diarrhea (BVD), parainfluenza (PI.sub.3), infectious bovine rhinotrocheitus (IBR), swine influenza, (H.sub.1N.sub.1,H.sub.3N.sub.2), fungi and parasites and combinations of the same. These organisms are consisted as opportunistic respiratory pathogens that may reside in the upper respiratory tract of healthy animals. Pasteurella and to a lesser extent Haemophilus and Mycoplasma species may cause bovine respiratory disease complex (BRDC) in cattle by the result of invasion of the lower respiratory tract after endogenous injections of the nasopharynx. In dairy or feedlot cattle, a variety of stressful situations such as shipment, weaning, viral infections, bad weather, change in weather, movement in feedlots, poor nutrition, and overcrowding can impair the competence of the immune system and the physical and immunological defenses of the animals. This allows greater numbers of microorganisms to make the journey from the nasopaharyngeal area to the lower respiratory tract to the interior of the lungs. This leads to the pneumonic respiratory disease complex, which includes the shipping fever complex in cattle. Transmission between animals is usually by airborne droplets or by food or water contamination. Once the microorganisms are established in the nasopharyngeal area, during inspiration the aerosols can result in downward carriage of the bacterial into the lower respiratory tract. This allows the organisms to attach to the bronchi and alveolar cells and to multiply causing pneumonia. Lung infections can lead to lesions with no clinical signs but lead to lower average daily gain. Animals can go off feed, become very ill rapidly and death can occur within hours. Morbidity can be very high and once one animal becomes ill the rest of the herd are easier to infect. This becomes a major concern for feedlots. Similar outbreaks occur in swine herds and flocks of birds such as chickens and turkeys. Current live vaccines have had limited success in protecting the animals against this complex. This may in part be due to the lack of immune protection in the nasopharyngal area. Although the group of respiratory viruses can weaken the animals and decease the immunological response of the host, it is the bacterial strains (usually Mannhiema hemolytica or Pasteurella multocida) that invade the lower respiratory tract leading to bronchopneumonia (BRD) that lead to disease and death of the animal. In both shipping fever pneumonia and enzootic pneumonia in cattle, the final common denominator in both types of disease are the bacterial agents. Bovine respiratory disease (BRD) is the leading cause of disease related loss in feedlots today. Financial losses attributed to BRD include mortality, medication, veterinary, and labor costs for treatment. Average costs for one treatment average $8.80 per head. Heifers treated for BRD have lower morbidity scores by 37.9%. Animals that are never treated average $11.48 per head higher in net return. The average daily gains differ between treated and untreated animals. The net profit averages $57.48 lower per head for treated animals. BRD has been listed as causing 20.6% of all steer deaths in feedlots.
Porcine respiratory disease complex is a major and similar type of disease affecting up to 90% of all swineherds. Mycoplasma hypopneumonia is the primary pathogen commonly associated with the complex secondary pathogens such as Pasteurella multocida types A and D and can cause clinical signs of high fever or impaired growth. Combinations of these organisms can lead to both increase in severity and duration of pneumonia in swine. Porcine reproduction and respiratory syndrome (PRRS) can be another major cause of pneumonia in swine. This can lead to severe reproduction disease with only minimal dose of virulent PRRS stains. Common causation agents of Swine respiratory disease can include PRRS virus, swine influenza (H1N1, H3N2) and Mycoplasma hypopneumoniae along with Haemophilus parasuis, Haemophilus suis, Haemophilus planopneumonia, Pasteurella (Mannhiema) haemolytica and Pasteurella multocida (types A & D). Estimating the total economic impact on the health of these animals is difficult. Pneumonic lung lesions may cause poor respiratory health in herds and may affect up to 70 percent of the pigs in a herd. Combinations of vaccinations for viruses and medication for bacteria are needed to help control these problems—timing of vaccination is always important. Medication must be applied at the proper time to minimize costs and damage to the animals.
Organisms such as Mycoplasma hypopneumoniae can be a cause an important chronic respiratory disease called “swine enzootic pneumonia” (SEP). This organism alone can produce severe pneumonia in swine and remains a significant threat to the swine industry.
Actinobacillus pleuropneumoniae causes “porcine pleuropneumoniae”, resulting in serious financial losses and death. Although vaccines have been developed, homologous protection has not been demonstrated. During the past years, 14 serotypes and 2 biotypes have been identified worldwide. Both growing and finishing pigs must be vaccinated to protect herds.
The primary effect of respiratory disease in swineherds is seen in reduced feed intake that leads to impaired growth. This leads to less uniformity in pigs, more mortality, less average daily gain, and less pigs per litter. Producers report that almost 14.4% of all herd placements develop respiratory disease. Costs increase for injecting vaccines and medication, and lower overall performance. Estimates have been made that reduced daily weight gain and antibiotics used to treat disease cost the Swine industry 467 million dollars annually. Over 39% of all deaths in grower-finisher pigs had been attributed to respiratory diseases in swine.